Expert Critique

Working the night shift can increase the incidence of type 2 diabetes. A recent study published in the February 2017 issue of Diabetes Care looked at 270,000 workers who had some experience of shift work, defined here as any work schedule that fell outside of the 9 a.m.-5 p.m. structure, and concluded that working more night shifts per month was associated with higher risk in developing the disease. The study also showed, however, that elevated type 2 diabetes risk did not apply to those who are permanent night shift workers. The researchers attributed this to the fact that permanent night shift workers may possess tendencies to practice a healthier lifestyle with lower alcohol consumption and higher levels of physical activity.

Nonetheless, other studies demonstrated that night shift work could lead to more unhealthy choices and behaviors. A meta-analysis from the fall 2017 issue of Obesity Reviews found that night shift workers are at higher possibility of developing obesity, specifically abdominal obesity. Those people who are permanent night workers demonstrated a 29% higher risk of obesity compared to rotating shift workers. Elevations in glucose can occur due to atypical eating times and sleeping practices that night shifts demand.

This article illustrates the importance of physicians becoming aware of these increased risks for type 2 diabetes so that they can adequate address these risks. Care providers could help assist patients who work night shifts in finding ways to manage their medications such as setting phone reminders and encouraging good sleep hygiene and exercise. In other words, understanding the unique needs of the patients who are on night shift might help improve dialogue and treatments accordingly.

Full Critique

Employees who work in shifts -- particularly the night shift -- are more likely to develop type 2 diabetes, according to a new study.

Published in February in the journal Diabetes Care, researchers analyzed approximately 270,000 patients who had some exposure to shift work, defined as any work schedule falling outside the conventional 9 a.m.-5 p.m. structure.

Compared with day workers, night shift workers were at higher multivariable-adjusted odds for type 2 diabetes, according to the study findings. The phenomenon affected those who worked night shifts rarely (OR 1.15 [95% CI 1.05 to 1.26]), some of the time (OR 1.18 [95% CI 1.05 to 1.32]), and frequently (OR 1.44 [95% CI 1.19 to 1.73]). Overall, working more night shifts per month was associated with higher type 2 diabetes odds than traditional day workers, including those who worked fewer than 3 night shifts per month (OR 1.24 [95% CI 0.90 to 1.68]), 3-8 per month (OR 1.11 [95% CI 0.90 to 1.37]), and more than 8 per month (OR 1.36 [95% CI 1.14 to 1.62]).

"We found that all shift workers were more likely to have type 2 diabetes, except for permanent night shift workers," said lead study author Celine Vetter, DPhil, a psychologist at the University of Colorado Boulder. "Those who reported working irregular or rotating shifts with usual night shifts were 44% more likely to have type 2 diabetes, after taking into account other established risk factors."

In contrast to previous findings, this most recent study found that elevated type 2 diabetes risk does not carry over to permanent night shift workers. Only those who worked night shifts for 10 years or less had a significantly higher type 2 diabetes likelihood than those who never worked night shifts. The elevated risk did occur in those who worked night shifts for less than 5 years (OR 1.37 [95% CI 1.11 to 1.68]) and for 5-10 years (OR 1.38 [95% CI 1.05 to 1.81], but not in those with more than 10 years of exposure (OR 1.15 [95% CI 0.95 to 1.38]). Study authors wrote that this could be explained by a tendency among permanent night shift workers "to exhibit some healthier lifestyle characteristics, including lower levels of alcohol intake and higher levels of physical activity, than other groups."

Other studies also show night shift work can foster risky behavior regardless of whether it is short-term, long-term, or permanent. A fall 2017 meta-analysis published in Obesity Reviews found that that night shift workers were at substantially greater risk of becoming obese or overweight compared with those who did not work the night shift (OR 1.23 [95% CI 1.17 to 1.29]). Shift workers had a higher frequency of developing abdominal obesity (OR 1.35) than other obesity types. Permanent night workers demonstrated a 29% higher risk than rotating shift workers (OR 1.43 versus 1.14).

"Shift work causes serious behavioral changes with physical activity, sleep, and eating time," said Shelly Tse Lap Ah, MB, PhD, of the Chinese University of Hong Kong, who co-authored the analysis. "At the same time, workers' endocrine and circadian systems respond to nocturnal activity accordingly. Also, individual susceptibility and adaptation highly affects the magnitude of adverse health effect from night work."

Another 2017 study showed that night shift work could directly affect blood glucose. Night shift workers who participated in the research had significant higher HbA1c levels compared with day workers and unemployed participants (8.23 ± 1.77% versus 7.58 ± 1.39% versus 7.54 ± 1.45%, P=0.01). According to study authors, there could be several factors underlying this result.

"As the workers are usually awake at night and sleep during the day, this may disrupt their biological clock," said co-author Sirimon Reutrakul, MD, of the Mahidol University Faculty of Medicine in Bangkok. "We know that eating and sleeping at a wrong time could cause elevated blood glucose. In addition, shift workers may not sleep as well, which is also related to glucose levels. Taking medications may be challenging, especially with timing. Fatigue also may interfere with the desire to exercise."

Researchers suggested that future research could more closely investigate links between work schedules, behavior, and health.

Clinical Implications

For physicians and their care teams, helping patients better understand, monitor, and control diabetes risk factors becomes particularly important when those patients engage in night shift work, be it occasional or full-time.

"There are things that individuals can do, even if they cannot change their work schedule or decrease their night shift work exposure," Vetter said. "There are a number of known risk factors for type 2 diabetes, such as low quality of diet, lack of physical activity, sleep debt, and elevated body mass index. Those are crucial when we are thinking about how to prevent type 2 diabetes."

Care providers can assist patients in finding strategies for managing health on a nontraditional schedule. Robust reminder systems for taking medication, for example, can be an effective tool.

"Recognizing that shift work may pose some barriers to glucose control and trying to work with an individual's schedule is a good start," said Reutrakul. "Encourage the patients to take their medicine. Use techniques that may work for the person, like setting a reminder on their phone. Encourage them to try to get good sleep by practicing good sleep hygiene, and help them try to be mindful about exercise. Having all these conversations with the patients should be helpful."

Ultimately, simply understanding that shift work in and of itself can affect health will help inform dialogues and treatment courses accordingly.

"An important take home message is that even after controlling for risk factors such as low quality of diet, lack of physical activity, sleep debt, and elevated BMI, we still saw an association between shift work and the likelihood of having type 2 diabetes," Vetter said.

The individuals interviewed for this article reported no conflicts of interest.

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